This invention relates to an apparatus and method for coating bundles of continuous filaments. More particularly it relates to coating bundles of freshly spun continuous filament glass fibers.
Traditionally, water or water-based sizings are sprayed or coated onto glass fibers as they are formed to lubricate and protect the filaments during subsequent processing steps. These steps may include initial wind-up, chopping, drying, re-winding, packaging, shipping, and finally unwinding into an end use. Since glass fibers are inherently flaw sensitive, any "uncoupled" composite process (where the formed glass must be handled before introducing the matrix resin) will require the use of such sizings and finishes on the glass roving. In addition to added water and chemicals, moisture and other contaminants from the surrounding atmosphere will also degrade the quality of glass fibers by rapidly adsorbing onto the high energy pristine glass surface.
Since all of these added surface species (whether applied intentionally or adsorbed from the atmosphere) tend to mask the glass surface, it is very difficult to wet and adhere matrix resins onto glass fibers in composite applications. This wetting and adhesion problem is especially important for viscous thermoplastic resins and systems without intensive mixing. Organometallic materials (e.g. silanes, titanates and chromates) are commonly added to the sizing formulation to overcome these problems. Although these three component systems (glass+sizing+resin) have been under development and optimization, evidence in the literature suggests that superior wetting and adhesion could be realized if all additives and contamination were kept away from the glass surface before the matrix resin is applied,